Self-sufficient air conditioning cools with sunlight

Principle of the absorption refrigerating machine coupled with photovoltaic

Developers of Siemens Corporate Technology are building a system consisting of a light collection system that captures solar heat and a photovoltaic unit for the power supply. © Siemens
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The sun can not only heat, it also cools - if you use your energy to operate an air conditioner according to the principle of the absorption chiller. A prototype of such a system has now been developed by Siemens researchers in Bangalore, India. Electricity for the operation and heat for the separation of the salt solution used thereby provides the sun. The system is thus completely self-sufficient and climate-friendly at the same time.

In the hot regions of the world, such as in India, air conditioning systems contribute significantly to CO2 emissions: about 60 percent of the electricity in Indian office buildings is consumed by air conditioning systems during the day. But that could change in the future. Siemens researchers have developed a system that uses solar heat to absorb heat from buildings, thereby cooling the rooms. The big advantage here: the whole thing is operated with an extremely compact solar system that fits on most office roofs. At the beginning of 2012, a pilot plant is to be installed on the roof of the Siemens building in Bangalore.

Salt as a key element

The solution is based on the well-tried principle of the absorption chiller. Usually a saline solution is used. Water serves as a refrigerant. Solar heat heats the water-salt mixture and separates the water as vapor from the salt solution. Subsequently, the water is condensed and pumped into an evaporator, which generates the cold. In the evaporator, there is negative pressure, so that even the low outside temperatures are sufficient to evaporate the water. The environment is deprived of heat, the room cooled. Subsequently, the steam is again bound to the salt solution. As the system operates in the cycle, the environment is permanently cooled. The photovoltaic power is needed to pump the water and saline solution through the system.

More compact photovoltaic system as a power source

Previous systems require an expensive and large photovoltaic system for this process, which can be found on the fewest office roofs. The Siemens researchers are now building a compact system and making better use of solar energy. The challenge is to get enough heat for the cooling process and power for the pump at the same time. One idea is to use a special liquid that extracts enough heat from the sunlight before it reaches the photovoltaic unit. For a compression refrigerator like in a refrigerator, the amount of electricity would be insufficient, but for the small pumps of the absorption refrigeration process.

The potential of this technology is huge: In India, the demand for office and commercial cooling by 2015 is estimated at around 31, 000 megawatts - the output of about 30 large coal-fired power plants

(Siemens, 10.06.2011 - NPO)